Presentation on theme: "Bio-Contaminants & Food Webs By: Patuxent Wildlife Research Center."— Presentation transcript:
Bio-Contaminants & Food Webs By: Patuxent Wildlife Research Center
Lesson 1 Review Points Using Science as Evidence When science is used as evidence it is important to identify possible sources of bias. Bias may be due to sampling bias or measurement bias. Background of DDT DDT is a pesticide used for mosquito control and pest control in agricultural crops. DDT accumulation in some bird species resulted in death, nervous system damage, and reproductive failure. As a result DDT was banned in the United States in 1972.
What are some sources of bias? Applying the results of a study too broadly (generalizing) Taking research results out of context Not taking a random sample Taking too small of a sample Measurement error
Lesson 2 Food Webs, Bioaccumulation, and Visualizing Data
Positive Aspects DDT Insecticide used to kill pests and damaging insects in Agriculture Commonly kills off mosquitoes, and has been used to help fight malaria.
What kind of damage can DDT cause to birds?
In the body of an animal, DDT is changed (metabolized) to DDE. DDE dissolves in fat, not in water, and is stored in fatty tissues. Thus, DDE tends to remain in the body and can cause several problems.
DDE: Kinds of Damage Reproductive failure (in birds- eggshell thinning) Immune system problems Nervous system damage Death
How does DDT move into lakes, streams and oceans?
After DDT is applied, some DDT volatizes, some remains on the plant, and some washes off the plant into the soil, eventually making its way to a a stream, river, or lake. The DDT that remains on the leaves of plants may be ingested by primary consumers such as insects and rodents. DDT that has washed into a waterbody, remains in the sediment or is consumed by bottom-feeding organisms or absorbed by fish gills and skin.
Is DDT still used today?
YES DDT is still used in some countries for insect control on crops. In countries where mosquitoes carry malaria, DDT is currently used for mosquito control.
What is a Food Web?
Food Web = A summary of the feeding relationships within an ecological community. ORGANIC DEBRIS Osprey Water Plants Sucker Bay Shrimp Trout Plankton Silverside
Food Chain = One thread of the food web ORGANIC DEBRIS Osprey Large Mouth Bass Crayfish
Cast of Food Web Characters Tertiary Consumers – Animals that eat animals that eat animals Secondary Consumers – Animals that eat animals that eat plants Primary Consumers – Animals that eat plants Primary Producers – Plants and Phytoplankton: organisms using the sun for energy
Why is food web knowledge important for understanding the impact of DDT on ospreys and eagles?
Ospreys and eagles are tertiary consumers and this makes them particularly vulnerable to DDT because of bioaccumulation and biomagnification.
What is bioaccumulation?
Bioaccumulation = the accumulation of a contaminant or toxin in or on an organism from all sources (e.g., food, water, air). An increase in the concentration of a chemical in a biological organism over time, compared to the chemical's concentration in the environment. Compounds accumulate in living things any time they are taken up and stored faster than they are broken down (metabolized) or excreted.
What is biomagnification?
Biomagnification = the increase in concentration of toxin as it passes through successive levels of the food web DDE accumulates at higher levels in organisms that are higher in the food chain
Biomagnification of a DDE in Aquatic Environment Tertiary Consumer 3-76 µg/g ww (fish eating birds) Level Amount of DDE in Tissue Secondary Consumers 1-2 µg/g ww (large fish) Primary Consumers (small fish) µg/g ww Primary Producers (algae and aquatic plants) 0.04 µg/g ww
Considering biomagnification, how could DDE harm an osprey?
Osprey Food Web Large Mouth Bass Crayfish Plant material and algae 3-76 µg/g ww 1-2 µg/g ww µg/g ww 0.04 µg/g ww DDE Concentration Osprey
Units of Measurement 1 gram = 1000 milligrams (mg) = 1,000,000 micrograms (µg) microgram (µg) = one millionth of a gram To describe concentrations: µg/g = number of micrograms (of toxin) per gram (of tissue) 2 µg/g DDE in egg content means there is 2 parts of DDE in 1,000,000 parts of an egg contents ww or wet weight refers to the fresh weight of animal tissue. dw or dry weight refers to the weight of animal tissue after it has been dried in an 65°C oven to remove all the water.
The Effects of DDE on Reproduction SpeciesEffect on Reproduction DDE: Critical Concentration (measured in egg contents) Bald EagleNone < 3µg/g 1 Bald EagleFailure 16 µg/g 1 OspreyFailure17.6 µg/g 2 Wiemeyer, S.N. et al., Organochlorine pesticide, polychlorobiphenyl, and mercury residues in bald eagles, , and their relationship to shell thinning and reproduction. Arch. Environ. Contam. Toxicol., 13, 529. Johnson, D.R. et al., DDT and PCB levels in Lake Coeur dAlene, Idaho osprey eggs, Bull. Environ. Contam. Toxicol., 13, 401.
High levels of DDE cause the female ospreys to lay eggs with thin eggshells. Thin eggshells have a greater chance of breaking, leading to embryo death. With high levels of DDE, female ospreys can also lay eggs that contain high enough concentration of DDE to prevent embryo development.
How is the impact of DDE on osprey and eagle reproduction measured?
One Method for Measuring the Impact of DDE on Osprey Reproduction Collect eggs from abandoned osprey nests. Measure the thickness of the eggshells. Measure the amount of DDE in the egg. Determine the association between eggshell thickness and DDE residue.
Visualizing the Data
If increased DDE concentrations causes increased eggshell thinning, how would you draw a graph showing the relationship between eggshell thinning and DDE concentration?
If DDE has no impact on eggshell thickness, what relationship would you expect to see between DDE levels and eggshell thickness?
If increased levels of DDE are associated with increased eggshell thickness, how would you make a graph showing the relationship between eggshell thickness and DDE concentration?
DDE reduces reproductive rates at moderate concentrations. At high concentrations it causes total reproductive failure. How would you make a graph showing the relationship between DDE concentration and reproductive success?